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mm,fs: Prevent page refcount overflow (CVE-2019-11487)

This commit is contained in:
Ben Hutchings 2019-05-05 15:44:05 +01:00
parent 83f5e0f1ef
commit ece5b4e4cd
6 changed files with 434 additions and 0 deletions
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5
debian/changelog vendored
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@ -1111,6 +1111,11 @@ linux (4.19.37-1) UNRELEASED; urgency=medium
- aio: store event at final iocb_put()
- Fix aio_poll() races
* tracing: Fix buffer_ref pipe ops
* mm,fs: Prevent page refcount overflow (CVE-2019-11487):
- mm: make page ref count overflow check tighter and more explicit
- mm: add 'try_get_page()' helper function
- mm: prevent get_user_pages() from overflowing page refcount
- fs: prevent page refcount overflow in pipe_buf_get
[ YunQiang Su ]
* [mips*r6] Re-enable CONFIG_JUMP_LABEL, which has been fixed in upstream.

52
debian/patches/bugfix/all/0001-mm-make-page-ref-count-overflow-check-tighter-and-mo.patch vendored Normal file
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@ -0,0 +1,52 @@
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 11 Apr 2019 10:06:20 -0700
Subject: mm: make page ref count overflow check tighter and more explicit
Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=9f6da5fd05577ef4a05c1744cc7098d0173823af
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-11487
commit f958d7b528b1b40c44cfda5eabe2d82760d868c3 upstream.
We have a VM_BUG_ON() to check that the page reference count doesn't
underflow (or get close to overflow) by checking the sign of the count.
That's all fine, but we actually want to allow people to use a "get page
ref unless it's already very high" helper function, and we want that one
to use the sign of the page ref (without triggering this VM_BUG_ON).
Change the VM_BUG_ON to only check for small underflows (or _very_ close
to overflowing), and ignore overflows which have strayed into negative
territory.
Acked-by: Matthew Wilcox <willy@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/mm.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e899460f1bc5..9965704813dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -915,6 +915,10 @@ static inline bool is_device_public_page(const struct page *page)
}
#endif /* CONFIG_DEV_PAGEMAP_OPS */
+/* 127: arbitrary random number, small enough to assemble well */
+#define page_ref_zero_or_close_to_overflow(page) \
+ ((unsigned int) page_ref_count(page) + 127u <= 127u)
+
static inline void get_page(struct page *page)
{
page = compound_head(page);
@@ -922,7 +926,7 @@ static inline void get_page(struct page *page)
* Getting a normal page or the head of a compound page
* requires to already have an elevated page->_refcount.
*/
- VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page);
+ VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page);
page_ref_inc(page);
}

56
debian/patches/bugfix/all/0002-mm-add-try_get_page-helper-function.patch vendored Normal file
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@ -0,0 +1,56 @@
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 11 Apr 2019 10:14:59 -0700
Subject: mm: add 'try_get_page()' helper function
Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=0612cae7ec6b79d2ff1b34562bab79d5bf96327a
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-11487
commit 88b1a17dfc3ed7728316478fae0f5ad508f50397 upstream.
This is the same as the traditional 'get_page()' function, but instead
of unconditionally incrementing the reference count of the page, it only
does so if the count was "safe". It returns whether the reference count
was incremented (and is marked __must_check, since the caller obviously
has to be aware of it).
Also like 'get_page()', you can't use this function unless you already
had a reference to the page. The intent is that you can use this
exactly like get_page(), but in situations where you want to limit the
maximum reference count.
The code currently does an unconditional WARN_ON_ONCE() if we ever hit
the reference count issues (either zero or negative), as a notification
that the conditional non-increment actually happened.
NOTE! The count access for the "safety" check is inherently racy, but
that doesn't matter since the buffer we use is basically half the range
of the reference count (ie we look at the sign of the count).
Acked-by: Matthew Wilcox <willy@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/mm.h | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9965704813dc..bdec425c8e14 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -930,6 +930,15 @@ static inline void get_page(struct page *page)
page_ref_inc(page);
}
+static inline __must_check bool try_get_page(struct page *page)
+{
+ page = compound_head(page);
+ if (WARN_ON_ONCE(page_ref_count(page) <= 0))
+ return false;
+ page_ref_inc(page);
+ return true;
+}
+
static inline void put_page(struct page *page)
{
page = compound_head(page);

155
debian/patches/bugfix/all/0003-mm-prevent-get_user_pages-from-overflowing-page-refc.patch vendored Normal file
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@ -0,0 +1,155 @@
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 11 Apr 2019 10:49:19 -0700
Subject: mm: prevent get_user_pages() from overflowing page refcount
Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=d972ebbf42ba6712460308ae57c222a0706f2af3
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-11487
commit 8fde12ca79aff9b5ba951fce1a2641901b8d8e64 upstream.
If the page refcount wraps around past zero, it will be freed while
there are still four billion references to it. One of the possible
avenues for an attacker to try to make this happen is by doing direct IO
on a page multiple times. This patch makes get_user_pages() refuse to
take a new page reference if there are already more than two billion
references to the page.
Reported-by: Jann Horn <jannh@google.com>
Acked-by: Matthew Wilcox <willy@infradead.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/gup.c | 45 ++++++++++++++++++++++++++++++++++-----------
mm/hugetlb.c | 13 +++++++++++++
2 files changed, 47 insertions(+), 11 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 0a5374e6e82d..caadd31714a5 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -153,7 +153,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
}
if (flags & FOLL_GET) {
- get_page(page);
+ if (unlikely(!try_get_page(page))) {
+ page = ERR_PTR(-ENOMEM);
+ goto out;
+ }
/* drop the pgmap reference now that we hold the page */
if (pgmap) {
@@ -296,7 +299,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
if (pmd_trans_unstable(pmd))
ret = -EBUSY;
} else {
- get_page(page);
+ if (unlikely(!try_get_page(page))) {
+ spin_unlock(ptl);
+ return ERR_PTR(-ENOMEM);
+ }
spin_unlock(ptl);
lock_page(page);
ret = split_huge_page(page);
@@ -480,7 +486,10 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
if (is_device_public_page(*page))
goto unmap;
}
- get_page(*page);
+ if (unlikely(!try_get_page(*page))) {
+ ret = -ENOMEM;
+ goto unmap;
+ }
out:
ret = 0;
unmap:
@@ -1368,6 +1377,20 @@ static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
}
}
+/*
+ * Return the compund head page with ref appropriately incremented,
+ * or NULL if that failed.
+ */
+static inline struct page *try_get_compound_head(struct page *page, int refs)
+{
+ struct page *head = compound_head(page);
+ if (WARN_ON_ONCE(page_ref_count(head) < 0))
+ return NULL;
+ if (unlikely(!page_cache_add_speculative(head, refs)))
+ return NULL;
+ return head;
+}
+
#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
int write, struct page **pages, int *nr)
@@ -1402,9 +1425,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
- head = compound_head(page);
- if (!page_cache_get_speculative(head))
+ head = try_get_compound_head(page, 1);
+ if (!head)
goto pte_unmap;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
@@ -1543,8 +1566,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
refs++;
} while (addr += PAGE_SIZE, addr != end);
- head = compound_head(pmd_page(orig));
- if (!page_cache_add_speculative(head, refs)) {
+ head = try_get_compound_head(pmd_page(orig), refs);
+ if (!head) {
*nr -= refs;
return 0;
}
@@ -1581,8 +1604,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
refs++;
} while (addr += PAGE_SIZE, addr != end);
- head = compound_head(pud_page(orig));
- if (!page_cache_add_speculative(head, refs)) {
+ head = try_get_compound_head(pud_page(orig), refs);
+ if (!head) {
*nr -= refs;
return 0;
}
@@ -1618,8 +1641,8 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
refs++;
} while (addr += PAGE_SIZE, addr != end);
- head = compound_head(pgd_page(orig));
- if (!page_cache_add_speculative(head, refs)) {
+ head = try_get_compound_head(pgd_page(orig), refs);
+ if (!head) {
*nr -= refs;
return 0;
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 9e5f66cbf711..5fb779cda972 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4299,6 +4299,19 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
page = pte_page(huge_ptep_get(pte));
+
+ /*
+ * Instead of doing 'try_get_page()' below in the same_page
+ * loop, just check the count once here.
+ */
+ if (unlikely(page_count(page) <= 0)) {
+ if (pages) {
+ spin_unlock(ptl);
+ remainder = 0;
+ err = -ENOMEM;
+ break;
+ }
+ }
same_page:
if (pages) {
pages[i] = mem_map_offset(page, pfn_offset);

162
debian/patches/bugfix/all/0004-fs-prevent-page-refcount-overflow-in-pipe_buf_get.patch vendored Normal file
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@ -0,0 +1,162 @@
From: Matthew Wilcox <willy@infradead.org>
Date: Fri, 5 Apr 2019 14:02:10 -0700
Subject: fs: prevent page refcount overflow in pipe_buf_get
Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=0311ff82b70fa12e80d188635bff24029ec06ae1
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-11487
commit 15fab63e1e57be9fdb5eec1bbc5916e9825e9acb upstream.
Change pipe_buf_get() to return a bool indicating whether it succeeded
in raising the refcount of the page (if the thing in the pipe is a page).
This removes another mechanism for overflowing the page refcount. All
callers converted to handle a failure.
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/fuse/dev.c | 12 ++++++------
fs/pipe.c | 4 ++--
fs/splice.c | 12 ++++++++++--
include/linux/pipe_fs_i.h | 10 ++++++----
kernel/trace/trace.c | 6 +++++-
5 files changed, 29 insertions(+), 15 deletions(-)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1989,10 +1989,8 @@ static ssize_t fuse_dev_splice_write(str
rem += pipe->bufs[(pipe->curbuf + idx) & (pipe->buffers - 1)].len;
ret = -EINVAL;
- if (rem < len) {
- pipe_unlock(pipe);
- goto out;
- }
+ if (rem < len)
+ goto out_free;
rem = len;
while (rem) {
@@ -2010,7 +2008,9 @@ static ssize_t fuse_dev_splice_write(str
pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
pipe->nrbufs--;
} else {
- pipe_buf_get(pipe, ibuf);
+ if (!pipe_buf_get(pipe, ibuf))
+ goto out_free;
+
*obuf = *ibuf;
obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
obuf->len = rem;
@@ -2033,11 +2033,11 @@ static ssize_t fuse_dev_splice_write(str
ret = fuse_dev_do_write(fud, &cs, len);
pipe_lock(pipe);
+out_free:
for (idx = 0; idx < nbuf; idx++)
pipe_buf_release(pipe, &bufs[idx]);
pipe_unlock(pipe);
-out:
kvfree(bufs);
return ret;
}
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -189,9 +189,9 @@ EXPORT_SYMBOL(generic_pipe_buf_steal);
* in the tee() system call, when we duplicate the buffers in one
* pipe into another.
*/
-void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
+bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
- get_page(buf->page);
+ return try_get_page(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_get);
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1586,7 +1586,11 @@ retry:
* Get a reference to this pipe buffer,
* so we can copy the contents over.
*/
- pipe_buf_get(ipipe, ibuf);
+ if (!pipe_buf_get(ipipe, ibuf)) {
+ if (ret == 0)
+ ret = -EFAULT;
+ break;
+ }
*obuf = *ibuf;
/*
@@ -1660,7 +1664,11 @@ static int link_pipe(struct pipe_inode_i
* Get a reference to this pipe buffer,
* so we can copy the contents over.
*/
- pipe_buf_get(ipipe, ibuf);
+ if (!pipe_buf_get(ipipe, ibuf)) {
+ if (ret == 0)
+ ret = -EFAULT;
+ break;
+ }
obuf = opipe->bufs + nbuf;
*obuf = *ibuf;
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -108,18 +108,20 @@ struct pipe_buf_operations {
/*
* Get a reference to the pipe buffer.
*/
- void (*get)(struct pipe_inode_info *, struct pipe_buffer *);
+ bool (*get)(struct pipe_inode_info *, struct pipe_buffer *);
};
/**
* pipe_buf_get - get a reference to a pipe_buffer
* @pipe: the pipe that the buffer belongs to
* @buf: the buffer to get a reference to
+ *
+ * Return: %true if the reference was successfully obtained.
*/
-static inline void pipe_buf_get(struct pipe_inode_info *pipe,
+static inline __must_check bool pipe_buf_get(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
- buf->ops->get(pipe, buf);
+ return buf->ops->get(pipe, buf);
}
/**
@@ -178,7 +180,7 @@ struct pipe_inode_info *alloc_pipe_info(
void free_pipe_info(struct pipe_inode_info *);
/* Generic pipe buffer ops functions */
-void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
+bool generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_nosteal(struct pipe_inode_info *, struct pipe_buffer *);
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6820,12 +6820,16 @@ static void buffer_pipe_buf_release(stru
buf->private = 0;
}
-static void buffer_pipe_buf_get(struct pipe_inode_info *pipe,
+static bool buffer_pipe_buf_get(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct buffer_ref *ref = (struct buffer_ref *)buf->private;
+ if (refcount_read(&ref->refcount) > INT_MAX/2)
+ return false;
+
refcount_inc(&ref->refcount);
+ return true;
}
/* Pipe buffer operations for a buffer. */

4
debian/patches/series vendored
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@ -177,6 +177,10 @@ bugfix/all/0012-aio-keep-io_event-in-aio_kiocb.patch
bugfix/all/0013-aio-store-event-at-final-iocb_put.patch
bugfix/all/0014-Fix-aio_poll-races.patch
bugfix/all/tracing-fix-buffer_ref-pipe-ops.patch
bugfix/all/0001-mm-make-page-ref-count-overflow-check-tighter-and-mo.patch
bugfix/all/0002-mm-add-try_get_page-helper-function.patch
bugfix/all/0003-mm-prevent-get_user_pages-from-overflowing-page-refc.patch
bugfix/all/0004-fs-prevent-page-refcount-overflow-in-pipe_buf_get.patch
# Fix exported symbol versions
bugfix/all/module-disable-matching-missing-version-crc.patch